I have done both dead's and squat's in the same workout, but I couldn't go all out on each one. I'd alternate them each week, starting with heavy squats then finishing with higher rep (12-15) deads at the end of the workout, then vice versa the next week. The reason I did this is because deads always leave my hams very sore, and so it was better for me to do them on leg day.
When I was doing this, I was on a Pull/Push/Legs split. It worked OK for me, but as soon as I went on to a 4 day schedule, I moved deads to back day.